pavelcherepan

OK then. Here's some thought: yes, going by uncertainty principle we can not predict anything, only as a probability. But on macroscopic scale, where QM effects are negligible and if we somehow find out the initial state of the Universe in a moment of time after QM effects were predominant, i.e. after Dark Ages and formation of stars and galaxies. Then would we be able to model and the evolution of Universe on a macroscopic scale from that time forward? Would we then not be able to predict future to some extent? Again, we're talking here only for the macroscopic scale.

That's some very inaccurate data you're referring to. Even on the Wikipedia article you can see that there was over 16000 earthquakes of mag 4+ in 2014. There's also a breakdown of earthquakes by month and magnitude so let's do a bit of rough calculation of total energy of earthquakes per month. To make it easier I took just integer values for magnitude and display them in terms of number of energy of Mag 4 earthquakes. In Richter scale the increase of magnitude by 1 point increases the energy of the earthquake 31.6 times (I used 32 for the ease of it) and we get these numbers as a result: It's not exactly accurate but still you can see that the total energy of earthquakes peaks sharply in April mostly due to one major mag 8.2 quake in Chile and multiple mag 7+ quakes. It peaks again in June and then in October-November. Obviously, from this data you can't conclude anything, maybe if you bothered and did a statistical calculation for, say 30-40 years' worth of earthquakes, maybe the data would show something but I rather doubt it. If, you're just looking at the total number of earthquakes, then, you'll see it peaking in April-June, but if you have a look at previous years, then there is not such discrepancy, it's pretty even for all months in 2013 and 2012, so your theory is not supported by the evidence.

Oh, yeah, definitely. I completely agree, I just forgot to correct my earlier post, where I said that assistants will see flashes simultaneously. Now that I've thought about it, it is obvious - we have already determined that in the FoR of train flashes will happen simultaneously and, thus the middle clock will flash, but since the front of the train is moving away from assistants and the back of the train - towards them, then in order for both rays to come to the middle at the same time in assistants' FoR the clock in the front must flash first and the clock in the back will flash later.

Yes, I agree again. But aren't all three clocks on the train in the same reference frame?

Ok, I get it. In fact I mentioned it in the previous post: But still that doesn't explain that clocks in different parts of the train would be showing a different time. If the flashes at both sides occur simultaneously, they would arrive in the middle at the same time and red/blue shift simply accounts for the observer moving to or from the source, right?

I had a look at Dark Energy section on the Hubble site and there is a slide show that explains briefly of how Dark Energy was discovered and what data it was based on. So we do have evidence that DE exists, we just don't yet know what it is.

Thanks for your reply, that's some interesting info. Still, I'm confused about your explanation. You're saying that it's incorrect to picture all three points of the train as being at 'same height' in a uniform gravitational field because it takes energy to move from the back of the train to the front. I totally agree with that. And yet, let's suppose I have two points A and B on the same height in a uniform gravitational field but in different spatial locations. If you want to move from point A to B you'd still require additional energy to counter the gravitational attraction and the amount of this extra energy will be (like in your explanation) proportional to the distance traveled. If all parts of the train start accelerating at the exact same time and at an exact same rate than I really see no reason why clocks in the back of the train would be going any differently from clocks in the middle and in the front.

Sorry about necroposting but it was just very interesting and i failed to notice the last post date. Thanks for the explanation too.

I don't have accurate number but liquid water in large amounts did appear back in Hadean and probably as far back as 4.4 billion years ago. Although the oceanic crust appeared is a whole different story. I think it means just that... immobile. There was no plate tectonics and so no part of crust was moving relative to another.

Hi there Dr. Funkenstein! 1) I think that science generally agrees that magma (it's not lava until it gets to the surface) moves up simply due to a density difference between the molten material of upper mantle and the Earth's generally solid crust. It's also generally not pushed though, it only comes up when there is an opportunity in the form of a crack, fault or some other sort of fracture. Until that moment the pressure of magma is generally not big enough to break surrounding hard rock and it gets accumulated in deep magma chambers. If no opportunity arises it just slowly solidifies over the course of millions of years and sometimes you can see results of this in the form of batoliths. 2) Now as far as gases are concerned, at high pressures of the upper mantle, even if material is partially or completely molten, the solubility of gases in the magma is huge. It is partially offset by the increase in temperature which decreases solubility, but the temperature rises slower than pressure as you go down. It's only when magma is approaching surface and the pressure drops significantly that de-gasification of magma begins. 3) Magma is not coming from the core. Except for small bits in the very upper part Earth's mantle is very much solid. Also it's general idea that heavy elements (iron and nickel) of which core mostly consists tend to slowly drift towards the center of the Earth, not the other way around due to gravitational forces. 4) Liquid magma forms either in so-called "hot spots" (Hawaii being a prime example), where a strong thermal flux is observed or in areas (subduction zones) where silicon-rich (and thus having lower melting point) material is present at the normal temperatures/pressures of the upper mantle. And I can't really comment on hydrocarbons being in contact with Mantle material because it just doesn't happen if only in minuscule amounts.

The trait may or may not appear and it may or may not be selected for depending on the conditions of the ecosystem of the time. I'm not sure how people can give even rough estimates of when that could happen. The farther you go in time the higher are the chances that the trait will appear, but at the same time your understanding of the conditions in which trait owner will live decreases dramatically. So it's just a guessing game. Maybe Megalodon-alike will re-appear in 5 million years, you never know

I might be all wrong but I see the situation as follows (and correct me if I'm wrong): 1) The train is at rest and clocks are synchronized 2) The train starts accelerating. Let's assume the acceleration is constant. Then by the equivalence principle of GR we can imagine both clocks and the middle observer being suspended at the same height above the gravitating mass that's big enough to account for the proper acceleration as can be measured by the accelerometer that the middle observer has on him/her (let's assume he/she does). 3) Both the front, rear and middle clocks will experience gravitational time dilation, but as the acceleration is the same for all of them all three clocks will still be synchronized. At the same time they (clocks) will be going slower compared to assistants' clocks who are outside and not experiencing any acceleration. 4) As acceleration finishes the train is again back to an inertial frame but the three clocks on the train and the ones that assistants have on them are still de-synchronized 5) Flashes occur at the both end of train. As the c is constant in any inertial reference frame, the middle observer will see flashes happen simultaneously. 6) If the middle observer had a spectrometer on him/her and analyzed light from both flashes he/she would see that the light coming from the front of the train has been shifted towards blue side of spectrum and the light coming from the back is red-shifted due to him/her moving towards or away from the respective source. 7) Now for the outside observers. Let's assume the train now is far enough from them that we can neglect the difference in distances that light has to travel to them from the front and rear of the train, respectively. Then they will see flashes happen simultaneously and being shifted depending on the direction the train is travelling relative to them. 8) After the experiment is finished the train decelerates to initial rest situation and as they move to the same reference plane as assistants are in, their clocks are coming back in synch. Outside observers and the middle observer compare notes and find out that they have different times recorded for the flash of the central clock while all clocks seem to be synchronized now. That's my reasoning, seems very similar to the twins paradox if I'm not terribly wrong somewhere. Correction: At the end of the experiment clocks on the train and clocks that assistants had may or may not be synchronized depending on how long the train has been travelling in an inertial frame at a speed close to the speed of light. If we assume that the light emission for both clocks is linked to an accelerometer so that the flash occurs exactly when the acceleration finishes and that receival of both flashes by the central observer triggers deceleration back to stationary, then in the end of the experiment clocks on the train and assistants' clocks will still be showing different times but the difference will be minute. If, on the other hand, the train spends significant amount of time travelling at close to the speed of light than de-synchronization will be noticeable.

A good way to start would be Feyman's lectures, Volume I if you haven't already tried that. Relativity starts from Chapter 15. The best thing about this book is how Feynman never omits steps in mathematical derivations and thus it's really easy to follow even if you're not very math-savvy like myself.

In regards to 3, what about mass-less photons? Probably a more correct way to put it would be to say "mass-energy" instead of just "mass". Number 2 also sounds a bit strange to me. The way you put it, it seems like the particles are prime and the energy is just their property, but in fact it's the energy that's basic, right?

Thanks Mordred! I'll try to find this book and have a read.

I'm pretty sure first thing you'll see will be 'spagettification' - there will be a huge difference in the gravitational pull between inner and outer edges of the rod so it will be torn apart, then again, and again, and again. It's possible to calculate the size of the final size of pieces that the rod will end up in - the size of pieces will be such that the difference in gravitational attaraction between inner/outer edges should be lower than the tensile strength of the material the rod is made of. Then, depending on whether said black hole is rotating or not, pieces will either just come to the event horizon and would sort of get 'stuck' there progressively getting dimmer and more redshfted until they aren't visible at all. Otherwise they will spiral towards black hole with ever increasing speed, getting hotter and hotter and maybe up to the stage of emitting x-rays and then again, cross the even horizon and disappear from view after some finite time.

I've seen quite a few satellites and they are normally easy to see a at night time, or rather evening/early morning. Same goes for the ISS, although it might be possible to see it in the middle of the day, but still it wouldn't match the description of "looked like a really bright star in the middle of the day". I think the best option would be to assume it was a weather balloon.

It might be a very stupid question but in a sense of particle-wave duality if we take a reference frame of a photon what would be the speed of the wave represented by that same photon in this particular reference frame?

I like this discussion, it's very interesting. Allow me to share some thoughts on the matter, although I don't claim to be trained in cosmology. The one definition of space that I like is "Space is where physical processes take place". I know, it's quite primary school'ish but I still like it. With that definition in mind I can't help but ask whether or not we can view space as merely a volume (or space-time as volume+time) in separation from the mass-energy that populates it? Does it even make sense to talk about 'empty space'? If we can talk about it on its own than it's all simple - we're just left with 3 spatial dimensions and one time dimension that defines space. If we can't view space in separation from mass-energy than space would also have a curvature as an inherent characterictic. Obviously, on a cosmological scale the space is considered flat but locally the curvature can be anything.

Chances of discovering ETs are quite low and the possible scientific effect is not likely to be immediate since any communication with other life species is limited by the speed of light. On the other hand Einstein@Home looks for possible gravitational wave sources as the last, still unverified consequence of GR. Even if such waves haven't been discovered yet, the project is quite successful in finding radio pulsars which is still quite a significant result.

I used to participate in CETI@Home but switched to Einstein@Home since it seems to me that there are more immediate benefits from the latter.

Hello everyone. It seems to me that too many established scientists nowadays like to bring up anthropic principle way too often. It's like this principle is a new deus ex machina - if you don't know how to explain something just bring up anthropic principle. Oh, yeah, and it's also infallable by the definition. Can you help me understand why it's so popular? Thanks!

My question is about the claim that it can be used in any source of water. I'm not an expert on the matter but imagine a normal situation where you attempt electrolysis of, say, sea water. You put a couple of electrodes into the water, connect them to a DC power source and it begins. After some time your electrodes become covered in a coating of ions, that have been dissolved in water previously and a little while after the whole sysytem will come to a halt because the coating will cause short-circuiiting or high power losses. I can't see why this won't be happening with nano-sized particles, which, since they produce a difference of electric potentials, would still have positive and negative poles. In fact, being nano-sized, their function would be impaired even quicker than that of a normal electrode.